In recent years, higher integration of a semiconductor element and increase in size have progressed, and there has been a demand for a thinner and miniaturized encapsulating resin package. Accompanied by this demand, a surface protection layer and an interlayer insulation film of the semiconductor element and a redistribution layer of a semiconductor package are needed to be formed of a material having more excellent electrical properties, thermal resistance, mechanical properties, and the like. Polyimide resins are one of the materials that may satisfy such demanded properties. For example, use of a photosensitive polyimide obtained by giving photosensitive properties to a polyimide resin has been considered. Use of the photosensitive polyimide has advantages that a pattern formation step is simplified and a complicated manufacturing step can be reduced (for example, see Patent Documents 1 and 2).
A film of a polyimide resin is usually formed by forming a thin film by a method such as a spin coat method using a solution (the so-called varnish) of a polyimide precursor (polyamide acid) obtained by reacting tetracarboxylic dianhydride with diamine, and performing thermal dehydration and ring closure (for example, see Non-Patent Document 1). The polyimide resin cures through this process of dehydration and ring closure. Unfortunately, the case of the polyimide resin using the polyimide precursor has a problem that volume shrinkage attributed to dehydration (imidization) occurs so that loss of a thickness and reduced dimensional accuracy occur in the time of curing. Moreover, a film formation step at a low temperature is desired lately, and there is a demand for a polyimide resin having an ability such that dehydration and ring closure of the polyimide resin is possible at a low temperature, and physical properties of the film after dehydration and ring closure bear comparison with those of a film obtained by dehydration and ring closure at a high temperature. However, curing of the polyimide precursor at a low temperature leads to imperfect imidizing. For this reason, the physical properties thereof deteriorate, for example, the cured film to be formed becomes fragile.
On the other hand, a photosensitive resin obtained by using other polymer that does not need to undergo dehydration and ring closure unlike the case of the polyimide precursor, and has high thermal resistance has been examined (for example, Non-Patent Document 2, Patent Documents 3 to 7). Particularly, in recent years, in application of the surface protection film and cover the coat layer for the semiconductor device having the redistribution layer, a positive-type photosensitive resin composition that can be developed by an alkaline aqueous solution and can form a resist pattern having higher thermal resistance has been demanded from the viewpoint of reduced environmental impact.    [Patent document 1] Japanese Unexamined Patent Publication SHO No. 49-115541    [Patent document 2] Japanese Unexamined Patent Publication SHO No. 59-108031    [Patent document 3] International Patent Publication No. WO2004/006020    [Patent document 4] Japanese Unexamined Patent Publication No. 2006-106214    [Patent document 5] Japanese Unexamined Patent Publication No. 2004-2753    [Patent document 6] Japanese Unexamined Patent Publication No. 2004-190008    [Patent document 7] Japanese Patent Publication No. 3812654    [Non-Patent Document 1] Saishin Poriimido Kiso to Ouyou, edited by Nihon Poriimido Kenkyuukai (2002)    [Non-Patent Document 2] J. Photopolym. Sci. Technol. 2005, vol. 18, p. 321-325